Alzheimer’s disease is a progressive neurodegenerative disorder defined by the accumulation of tau proteins aggregates in the brain. Soluble oligomers of aggregated tau and insoluble amyloid fibrils cause neurotoxicity and lead to neuronal death. No effective therapy or early diagnostic method is presently available to stop or slow down the progression of the resulting cognitive decline. Therapeutic efforts are targeting all the players involved in the formation and accumulation of aberrant tau protein. The use of antibodies against “pathogenic” tau has also been proposed, and preliminary experiments conducted on animal models have shown promising results. In this study, R. Abskharon et al. discovered a monoclonal antibody (M204) that binds oligomeric tau, but not tau monomers or fibrils. Soluble oligomers of aggregated tau accompany the accumulation of insoluble amyloid fibrils and are thought to drive the spread of tau pathology by seeding, which promotes the aggregation of natively folded tau. The researchers engineered also a single-chain variable-fragment (scFv) which inhibits seeding of tau oligomers induced by ionic liquid 15(IL15). Single-chain antibodies, due to their reduced size, can more easily distribute into tissues compared to full-length antibodies.
To determine which tau sequences are recognized by the M204 antibody, the researchers conducted an epitope mapping experiment. A microarray was fabricated using a library of biotinylated amyloid peptides incubated with Neutravidin. The peptide-neutravidin complex was then printed on ONCYTE® Film slides and interrogated with monoclonal antibody M204.
Different conformational states were also described for the monoclonal single-chain variable-fragment (scFv): monomeric, dimeric, and trimeric conformers were observed. While all three conformational states can bind to tau oligomers, the dimer showed increased inhibition of seeding. Structural studies revealed that the dimer increased inhibitory activity is associated with conformational changes supporting a stronger binding to tau oligomers. These findings suggest that M204-scFv targets pathological tau structures and may have potential as an early-stage diagnostic for AD and tauopathies, and also could guide the development of promising therapeutic antibodies.
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